Modified resin for molded article and golf ball

ABSTRACT

The present invention is a modified resin for a molded article obtained by modifying an ethylene/unsaturated carboxylic acid copolymer with guanidine carbonate, wherein a melt flow rate of the ethylene/unsaturated carboxylic acid copolymer is 20 (g/10 minutes) or more and 600 (g/10 minutes) or less.

TECHNICAL FIELD

The present invention relates to a modified resin for a molded article and a golf ball.

BACKGROUND ART

In recent years, polyolefin resins such as ethylene homopolymers, copolymers of ethylene and another olefin, and copolymers of ethylene and an unsaturated carboxylic acid have been used in various fields. For example, a polyolefin resin blended with magnesium hydroxide, aluminum hydroxide or the like is excellent in flame retardancy, and is therefore used as a coating material for electric wires or as a member of electric and electronic devices. Modification of a polyolefin resin is widely performed by adding acid-modification or a basic compound according to an intended purpose.

As a resin to which a basic compound is added, for example, Patent Literature 1 discloses a flame retardant resin composition containing a salt of a guanidine compound of acid-modified polyolefin. It is described that by using the flame retardant resin composition, excellent mechanical properties as well as flame retardancy are provided.

Patent Literature 2 discloses an ethylene-vinyl ester copolymer saponified product and an ethylene-vinyl ester copolymer saponified product composition containing a basic amine compound. It is described that a material containing the composition is useful for a multilayer structure because of its improved adhesion to a polyester resin.

Patent Literature 3 discloses a polyolefin resin composition obtained by adding guanidine phosphate to a polyolefin. It is described that by the polyolefin resin composition, excellent mechanical properties can be realized while suppressing generation of corrosive gas during combustion.

On the other hand, an ionomer obtained by neutralizing a copolymer of ethylene and (meth) acrylic acid with a metal ion has a high hardness and an impact resilience coefficient, and is therefore used in an elastic material layer constituting a golf ball or the like (see Patent Literature 4). A multilayer golf ball such as a two-piece ball, a three-piece ball and a four-piece ball is the most common among golf balls, in which a core portion at the center is coated with a plurality of elastic material layers and an outermost layer cover is provided.

In a multilayer golf ball, materials of a core, a cover layer and a layer (intermediate layer) between the core and the cover layer, affect a repulsive force of the ball, initial velocity, flight distance, spin performance and ball hitting feeling. In general, a butadiene rubber is used for the core, and an urethane resin and ionomer resin is used for the cover layer, and an ionomer resin is used for the intermediate layer. A repulsive force, initial velocity, flight distance, spin performance and ball hitting feeling characteristic of respective golf ball brands are adjusted by selecting and combining the materials used for respective layers appropriately.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2007-321024 -   Patent Literature 2: JP 2012-107197 -   Patent Literature 3: JP H06-25476 -   Patent Literature 4: JP H11-299933

SUMMARY OF THE INVENTION Technical Problem

However, there is room for further improvement in the impact resilience coefficient, hardness and flexural stiffness, so as to use a resin having excellent mechanical properties described in the above patent literatures as a material of a ball such as a golf ball. The present invention has been invented in view of the above circumstances. The object of the present invention is to provide a modified resin for a molded article having an excellent impact resilience coefficient, hardness and flexural stiffness, and a golf ball containing the modified resin for a molded article.

Solution to the Problem

The inventors of the present invention have found that a modified resin obtained by modifying an ethylene/unsaturated carboxylic acid copolymer having a melt flow rate within a specific range with at least one guanidine compound selected from guanidine derivatives and salts thereof has an excellent impact resilience coefficient, hardness and flexural stiffness, and have accomplished the present invention.

Namely, the modified resin for a molded article of the present invention is a modified resin for a molded article obtained by modifying an ethylene/unsaturated carboxylic acid copolymer with at least one guanidine compound selected from guanidine derivatives and salts thereof, wherein a melt flow rate of the ethylene/unsaturated carboxylic acid copolymer is 20 (g/10 minutes) or more and 600 (g/10 minutes) or less.

The melt flow rate (hereinafter referred to as MFR) is a value measured according to the Japanese Industrial Standard: JIS K7210 (1999) at a temperature of 190° C. and a loaded weight of 2160 g.

The ethylene/unsaturated carboxylic acid copolymer is preferably an ethylene/(meth) acrylic acid copolymer.

A content of a constituent unit derived from the unsaturated carboxylic acid in the ethylene/unsaturated carboxylic acid copolymer is preferably 10% by mass or more and 30% by mass or less with respect to the total content of constituent units of the ethylene/unsaturated carboxylic acid copolymer.

The ratio (B/A) of the total number of moles (B) of the guanidino group or guanidinium ion in the guanidine compound to the total number of moles (A) of the carboxyl group contained in the ethylene/unsaturated carboxylic acid copolymer in the modified resin for a molded article, is preferably 0.05 or more and 0.8 or less.

The guanidine salt is preferably guanidine carbonate.

The modified resin for a molded article is preferably a modified resin for a molded article, which is obtained by melt kneading the ethylene/unsaturated carboxylic acid copolymer and at least one guanidine compound selected from guanidine derivatives and salts thereof.

The golf ball of the present invention contains the modified resin for a molded article of the present invention.

Advantageous Effects of the Invention

According to the present invention, a modified resin for a molded article and a golf ball which are excellent in an impact resilience coefficient, hardness and flexural stiffness, can be obtained.

DESCRIPTION OF THE INVENTION

Hereinafter, the modified resin for a molded article and the golf ball of the present invention are described.

[Modified Resin for a Molded Article]

The modified resin for a molded article according to the present invention is a modified resin for a molded article obtained by modifying an ethylene/unsaturated carboxylic acid copolymer with at least one guanidine compound of guanidine derivatives and salts thereof, wherein MFR of the ethylene/unsaturated carboxylic acid copolymer is 20 (g/10 minutes) or more and 600 (g/10 minutes) or less.

From the viewpoint of improving the impact resilience coefficient, hardness and flexural stiffness, MFR of the ethylene/unsaturated carboxylic acid copolymer according to the present embodiments of the present invention, is more preferably 20 (g/10 minutes) or more and 500 (g/10 minutes) or less, even more preferably 20 (g/10 minutes) or more and 300 (g/10 minutes) or less.

The number average molecular weight (Mn) is preferably about 10,000 or more and about 30,000 or less in terms of polystyrene.

From the viewpoint of improving the impact resilience coefficient, hardness and flexural stiffness, the molar ratio of the total number of moles of the guanidino group and guanidinium ion in the guanidine compound to the total number of moles of the carboxyl group derived from the unsaturated carboxylic acids contained in the ethylene/unsaturated carboxylic acid copolymer, is preferably 0.05 or more and 0.8 or less, more preferably 0.05 or more and 0.7 or less, and even more preferably 0.05 or more and 0.6 or less.

(Ethylene/Unsaturated Carboxylic Acid Copolymer)

The ethylene/unsaturated carboxylic acid copolymer in the modified resin for a molded article according to the present embodiments of the present invention is not limited to a copolymer consisting only of ethylene and an unsaturated carboxylic acid, and may be a multi-component copolymer in which the copolymer is copolymerized with arbitrary another copolymer component.

The unsaturated carboxylic acid in the ethylene/unsaturated carboxylic acid copolymer includes a C₄₋₈ unsaturated carboxylic acid such as acrylic acid, methacrylic acid, ethacrylic acid, fumaric acid, crotonic acid, maleic acid, itaconic acid, monomethyl maleate, monoethyl maleate, maleic anhydride and itaconic anhydride, and the like. Particularly preferable is acrylic acid or methacrylic acid. The unsaturated carboxylic acid may be one type or two or more types.

The arbitrary another copolymer component includes, for example, an unsaturated carboxylic acid ester such as methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, dimethyl maleate and diethyl maleate; an unsaturated hydrocarbon such as propylene, butene, 1,3-butadiene, pentene, 1,3-pentadiene and 1-hexene; a vinyl ester such as vinyl acetate and vinyl propionate; an oxide such as vinyl sulfate and vinyl nitrate; a halide such as vinyl chloride and vinyl fluoride; a vinyl group-containing primary or secondary amine compound; carbon monoxide; sulfur dioxide; and the like.

The ethylene/unsaturated carboxylic acid copolymer may be any of a block copolymer, a random copolymer and a graft copolymer. From the viewpoint of industrial availability, a binary random copolymer, a ternary random copolymer, a graft copolymer of a binary random copolymer or a graft copolymer of a ternary random copolymer may be preferably used. More preferable is a binary random copolymer or a ternary random copolymer.

—Content of Constituent Unit Derived from Unsaturated Carboxylic Acid—

A content of a constituent unit derived from the unsaturated carboxylic acid in the ethylene/unsaturated carboxylic acid copolymer, is preferably 10% by mass or more and 30% by mass or less, more preferably 12% by mass or more and 26% by mass or less, and even more preferably 14% by mass or more and 22% by mass or less, with respect to the total content of constituent units of the ethylene/unsaturated carboxylic acid copolymer.

The above arbitrary another copolymer component may be copolymerized in a proportion of generally 15 mol % or less, preferably 10 mol % or less. Such an ethylene/unsaturated carboxylic acid copolymer is not particularly limited, but is preferably obtained by high-pressure radical copolymerization.

(Guanidine Compound)

In the present invention, the guanidine compound means a guanidine derivative (including guanidine) and a salt thereof.

The guanidine compound includes, for example, guanidine; a C₁₋₂₀ alkyl substituted guanidine (e.g. N-methyl or N-ethylguanidine, 1,3-dimethyl or 1,3-diethylguanidine, etc.); an aromatic guanidine (e.g. phenylguanidine, diphenylguanidine, etc.); a biguanide compound (e.g. biguanide, N-methylbiguanide, N-benzoylbiguanide, N-phenylbiguanide, cyanobiguanide, etc.); a guanyl C₁₋₂₀ alkyl urethane (e.g. guanylmethylurethane, guanylethylurethane, etc.); and another guanidine derivative (e.g. aminoguanidine, dicyanoguanidine, guanyl (thio)urea, cyanoguanyl (thio)urea, etc.); and hydrochloride, chlorate, perchlorate, hydrobromide, hydroiodide, sulfate, sulfite, phosphate, nitrate, carbonate, and a salt of an organic acid (e.g. formic acid, acetic acid, propionic acid, sulfonic acid) of the above listed guanidine compound. Preferable are guanidine, a C₁₋₂₀ alkyl guanidine, an aromatic guanidine and a carbonate thereof. Most preferable is guanidine carbonate.

(Optional Component)

To the modified resin for a molded article of the present invention, various additives may be optionally blended, such as another thermoplastic resin, a tackifying resin, a wax, an antioxidant, a weathering stabilizer, a light stabilizer, a heat stabilizer, an ultraviolet ray absorbent, a lubricant, a pigment, a dye, an inorganic filler, and the like.

[Method of Producing the Modified Resin for a Molded Article]

The modified resin for a molded article of the present invention can be prepared by adding and melt kneading the ethylene/unsaturated carboxylic acid copolymer, the guanidine compound such as guanidine carbonate, and the optional component, if necessary. The melt kneading temperature is preferably 50 to 300° C., more preferably 100 to 250° C. from the viewpoint of the melting temperatures and decomposition temperatures of the ethylene/unsaturated carboxylic acid copolymer and the guanidine compound.

A melt kneading apparatus is not particularly restricted, but includes, for example, a batch kneader (for example, Banbury Mixer [Product name, Farrel Corporation] and a kneader), a continuous kneader (for example, FCM [Product name, Farrel Corporation], LCM [Product name, Kobe Steel, Ltd.] and CIM [Product name, Nippon Steel Corporation], a single screw extruder and a twin screw extruder.

The resin composition containing the modified resin for a molded article of the present invention is excellent in the impact resilience coefficient, hardness and flexural stiffness. Therefore, the resin composition is useful for a ball, a toy member, an automobile member, a building member, a film, a sheet article or the like that requires such characteristics, particularly for a golf ball. Moreover, the resin composition may be blended with another resin such as nylon, PET and PBT, as a modifier.

[Golf Ball]

The golf ball of the present invention can be prepared by melt kneading and molding a material in which the modified resin for a molded article of the present invention and the optional component, if necessary, are blended. For example, it can be used as a one-piece ball material, a core material of the golf ball, or a cover material of the golf ball. Regarding the cover material, it can be used not only as a cover material of a two-piece ball, but also as an outer cover material or an inner cover material of a double cover ball.

EXAMPLE

Hereinafter, the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the specific examples shown below.

[Raw Material]

(A) Ethylene/Unsaturated Carboxylic Acid Copolymer

(a1) Ethylene/methacrylic acid copolymer (ethylene:methacrylic acid=80:20 by mass ratio (a content of a constituent unit derived from ethylene in the ethylene/unsaturated carboxylic acid copolymer is 80% by mass, and a content of a constituent unit derived from the unsaturated carboxylic acid is 20% by mass), MFR=60 (g/10 minutes)).

(a2) Ethylene/acrylic acid copolymer (ethylene:acrylic acid=82:18 by mass ratio (a content of a constituent unit derived from ethylene in the ethylene/unsaturated carboxylic acid copolymer is 82% by mass, and a content of a constituent unit derived from the unsaturated carboxylic acid is 18% by mass), MFR=60 (g/10 minutes)).

(B) Guanidine Carbonate (Tokyo Chemical Industry Co., Ltd.)

[Physical Property Measurement Method]

An impact resilience coefficient, hardness and flexural stiffness were measured as follows.

(Impact Resilience Coefficient)

A sheet having a size of 150 mm×150 mm×3 mm thick was prepared using the modified resin for a molded article and a hot press machine set at 160° C. A test piece having a layer thickness of about 13 mm (a diameter of the test piece: 29±0.5 mm) was prepared using a hot press machine set at 140° C. again by stacking six sheets obtained by punching the obtained sheet into a circle shape. This test piece was stored in an atmosphere of 23° C. and 50% relative humidity for 2 weeks. Then, the impact resilience coefficient was measured using this test piece with the Lupke impact resilience tester. The measurement condition was based on the Japanese Industrial Standard: JIS K6255: 2013.

(Shore D Hardness)

A sheet having a size of 150 mm×150 mm×3 mm thick was prepared using the modified resin for a molded article and a hot press machine set at 160° C. A test piece was prepared by punching the obtained sheet into a strip shape having a width of 20 mm and a length of 100 mm. This test piece was stored in an atmosphere of 23° C. and 50% relative humidity for 2 weeks. Then, the two sheets were stacked, and the hardness (Shore D) was measured with an Asker automatic rubber hardness meter P1-D type. The measurement condition was based on the Japanese Industrial Standard: JIS K7215: 1986.

(Flexural Stiffness)

A sheet having a size of 150 mm×150 mm×3 mm thick was prepared using the obtained modified resin for a molded article and a hot press machine set at 160° C. A test piece was prepared by punching the obtained sheet into a strip shape having a width of 20 mm and a length of 100 mm. This test piece was stored in an atmosphere of 23° C. and 50% relative humidity for 2 weeks. Then, the flexural stiffness was measured using this test piece. The measurement condition was based on the Japanese Industrial Standard: JIS K7106: 1995.

<Modified Resin for a Molded Article Obtained by Modifying an Ethylene/Methacrylic Acid Copolymer>

At first, examples are described in which an ethylene/methacrylic acid copolymer is modified.

Example 1-1

An ethylene/methacrylic acid copolymer modified with guanidine carbonate (a modified resin for a molded article) was obtained by adding 76.0 g of an ethylene/methacrylic acid copolymer (a1) and 1.33 g (1.7% by mass) of guanidine carbonate into LABO PLASTOMILL (product name “LABO PLASTOMILL 10C-100”, Toyo Seiki Seisakusho Co., Ltd.), followed by kneading the mixture at 220 to 230° C. and at 50 rpm for 6 to 12 minutes. The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer was 0.083.

Example 1-2

A modified resin for a molded article was obtained in the same manner as in Example 1-1 except that the content of guanidine carbonate was 2.65 g (3.4% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer was 0.17.

Example 1-3

A modified resin for a molded article was obtained in the same manner as in Example 1-1 except that the content of guanidine carbonate was 3.98 g (5.0% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer was 0.25.

Example 1-4

A modified resin for a molded article was obtained in the same manner as in Example 1-1 except that the content of guanidine hydrochloride was 5.30 g (6.5% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer was 0.33.

Example 1-5

A modified resin for a molded article was obtained in the same manner as in Example 1-1 except that the content of guanidine hydrochloride was 7.97 g (9.5% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer was 0.50.

Comparative Example 1-1

An ethylene/methacrylic acid copolymer (a1) was not modified with guanidine carbonate (B).

Table 1 shows the physical properties measured for Examples 1-1 to 1-5 and Comparative Example 1-1. “Guanidinium/acid group” in Table 1 means the molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/methacrylic acid copolymer.

TABLE 1 Content of Impact guanidine Guanidinium/ resilience Shore D Flexural carbonate acid group coefficient hard- stiffness (% by mass) (molar ratio) (%) ness (MPa) Example 1.7 0.083 58 68 230 1-1 Example 3.4 0.17 63 70 330 1-2 Example 5.0 0.25 65 70 400 1-3 Example 6.5 0.33 68 71 470 1-4 Example 9.5 0.50 68 73 560 1-5 Compar- — — 52 65 130 ative Example 1-1

As shown in Table 1, the ethylene/methacrylic acid copolymers modified with guanidine carbonate in Examples 1-1 to 1-5 have higher impact resilience coefficient, Shore D hardness and flexural stiffness, compared with the unmodified copolymer in Comparative Example 1-1.

<Modified Resin for a Molded Article Obtained by Modifying an Ethylene/Acrylic Acid Copolymer>

Next, examples are described in which an ethylene/acrylic acid copolymer is modified.

Example 2-1

An ethylene/acrylic acid copolymer modified with guanidine carbonate (a modified resin for a molded article) was obtained by adding 74.0 g of an ethylene/acrylic acid copolymer (a2) and 1.39 g (1.8% by mass) of guanidine carbonate into LABO PLASTOMILL (product name “LABO PLASTOMILL 10C-100”, Toyo Seiki Seisakusho Co., Ltd.), followed by kneading the mixture at 220 to 230° C. and at 50 rpm for 6 to 12 minutes. The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/acrylic acid copolymer was 0.083.

Example 2-2

A modified resin for a molded article was obtained in the same manner as in Example 2-1 except that the content of guanidine carbonate was 4.17 g (5.3% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/acrylic acid copolymer was 0.25.

Example 2-3

A modified resin for a molded article was obtained in the same manner as in Example 2-1 except that the content of guanidine carbonate was 8.34 g (10.7% by mass). The molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/acrylic acid copolymer was 0.50.

Comparative Example 2-1

An ethylene/acrylic acid copolymer (a2) was not modified with guanidine carbonate.

Table 2 shows the physical properties measured for Examples 2-1 to 2-3 and Comparative Example 2-1. “Guanidinium/acid group” in Table 2 means the molar ratio of the guanidinium ion in the modified resin for a molded article to the total number of moles of the carboxyl group in the ethylene/acrylic acid copolymer in the modified resin for a molded article.

TABLE 2 Content of Impact guanidine Guanidinium/ resilience Shore D Flexural carbonate acid group coefficient hard- stiffness (% by mass) (molar ratio) (%) ness (MPa) Example 1.8 0.083 50 66 120 2-1 Example 5.3 0.25 65 71 330 2-2 Example 10.7 0.50 69 73 470 2-3 Compar- — — 38 60 50 ative Example 2-1

As shown in Table 2, the ethylene/acrylic acid copolymers modified with guanidine carbonate in Examples 2-1 to 2-3 have higher impact resilience coefficient, Shore D hardness and flexural stiffness, compared with the unmodified sodium ionomer in Comparative Example 2-1.

As described above, the resin obtained by modifying the ethylene/unsaturated carboxylic acid copolymer with guanidine carbonate of the present invention has an excellent impact resilience coefficient, hardness and flexural stiffness.

The present application claims priority based on Japanese Patent Application No. 2018-025242 filed on Feb. 15, 2018, the entire disclosure of which is incorporated herein. 

1. A modified resin for a molded article obtained by modifying an ethylene/unsaturated carboxylic acid copolymer with at least one guanidine compound selected from guanidine derivatives and salts thereof, wherein a melt flow rate of the ethylene/unsaturated carboxylic acid copolymer is 20 (g/10 minutes) or more and 600 (g/10 minutes) or less.
 2. The modified resin for a molded article according to claim 1, wherein the ethylene/unsaturated carboxylic acid copolymer is an ethylene/(meth) acrylic acid copolymer.
 3. The modified resin for a molded article according to claim 1, wherein a content of a constituent unit derived from the unsaturated carboxylic acid in the ethylene/unsaturated carboxylic acid copolymer is 10% by mass or more and 30% by mass or less with respect to the total content of constituent units of the ethylene/unsaturated carboxylic acid copolymer.
 4. The modified resin for a molded article according to claim 1, wherein the ratio (B/A) of the total number of moles (B) of the guanidino group or guanidinium ion in the guanidine compound to the total number of moles (A) of the carboxyl group contained in the ethylene/unsaturated carboxylic acid copolymer in the modified resin for a molded article, is 0.05 or more and 0.8 or less.
 5. The modified resin for a molded article according to claim 1, wherein the guanidine salt is guanidine carbonate.
 6. The modified resin for a molded article according to claim 1, which is obtained by melt kneading the ethylene/unsaturated carboxylic acid copolymer and at least one guanidine compound selected from guanidine derivatives and salts thereof.
 7. A golf ball comprising the modified resin for a molded article according to claim
 1. 